Support tonicExampleFilename in package.json to customize the Tonicdev link in npm

https://tonicdev.uservoice.com/knowledgebase/articles/765846-how-do-i-customize-the-example-for-my-npm-package

> You can also put the example in a separate file, if you prefer, and then add this property instead:
> 
> "tonicExampleFilename": "example.js"
> 
> If you want to read more about the ﻿npm﻿/tonic﻿ integration, check out this blog post. 
